The present invention relates to a shut-off nozzle for injection molding of fluid plastics. The improved nozzle is connected to the barrel of an injection molding machine and is in selective communication with the sprue channel or bushing of a molding cavity. The improved nozzle is positively operated to fully open or fully close during transfer of the fluid plastic or plastic melt from the molding machine to the molding cavity.
Shut-off nozzles for injection molding of fluid plastics are not new. U.S. Pat. No. 3,401,426, Sept. 1968, Evans, discloses an injection molding machine having an integrally connected nozzle (N) with an axial plunger (28) relatively reciprocable between compression and decompression strokes and intended to prevent premature drool of plastic between injection shot-cycles. U.S. Pat. No. 3,500,501, March 1970, Johansson, discloses a nozzle shut-off device and acknowledges various forms of prior art devices employed to interrupt the flow of molten material from the nozzle into the mold sprue.
A publication, Plastics Machinery & Equipment Magazine, July 1976, Vol. 5, No. 7, at page 10, reviews several contemporary nozzle designs for injection molding of thermoplastics.
It has now been found that a shut-off nozzle for an injection molding machine need not be complex, may be relatively inexpensive to install, maintain and operate using precision fabricated and engineered components, and will satisfactorily perform with realistically chosen and reasonable operating parameters.